DFT study on the reaction of NO oxidation on a stepped gold surface

The oxidation of NO to NO 2 by atomic or molecular oxygen on the stepped Au(3 2 1) surface has a low energetic cost with GGA/PW91 computed energy barriers of 0.07 and 0.25 eV, respectively. These barriers are significantly smaller than the barriers for dissociation of molecular oxygen and for desorption of NO 2, which have values of about 1.0 eV. The NO oxidation either with atomic or molecular oxygen on the stepped Au(3 2 1) surface was studied by means of DFT calculations (GGA/PW91). A periodic supercell approach was used to model the gold stepped surface and the kinetic profiles of the reactions were determined with the dimer approach. It was found that the co-adsorption of NO and O occurs preferentially with these species interacting with top and hollow sites nearby the steps, respectively. In the case of co-adsorbed NO and O 2 species, the most stable configuration on the surface is a ONOO* intermediate. The NO 2 product adsorbs strongly on the Au(3 2 1) surface ( E ads = −1.10 eV) also nearby the step. The reaction of NO oxidation by atomic oxygen has an energy cost of 0.07 eV, whereas moderate-low energy barriers of 0.21 and 0.25 eV were computed for the reaction with molecular oxygen, via the ONOO* intermediate, following Elay–Rideal (ER) or Langmuir–Hinshelwood (LH) mechanisms, respectively. The reaction route following the ER mechanism is energetically more favorable since it is unnecessary to overcome the very high barriers (∼1 eV) needed for NO 2 desorption and for dissociation of molecular oxygen in the cases of NO reaction via LH mechanism and NO oxidation with atomic oxygen, respectively.